In the future a group of one-hundred humans land on the earth-like planet Dextra, only to find that the flora and fauna are incompatible with earth lifeforms. The DNA of everything on the planet twists in the opposite direction. So people can't eat any of the food and are dependant on growing the earth crops and raising earth animals, which is a battle. The story begins several hundred years after this first colony, with different groups of people inhabiting the planet. Mark Turner and Meriam, whose impending marriage was arranged by their parents, are on an exploration trip to one of the frontier areas - and come across something very strange. Although humans can't eat any of the Dextran creatures they have trained some of them to be basically slaves, small ape-like creatures. But these creatures mysteriously appeared - and are replaced by more advanced lifeforms which emerge from the wilderness every few years. The newest version are called Fauns and resemble the creatures from Greek Mythology. There are also Centaurs. It turns out that the planet is creating these creatures in order to adapt to the human invasion but there's a price for both sides.

This is an interesting book and reads like an Edgar Rice Burroughs novel (as many of those yellow-spined DAW books from the 70's do).